Field of the Invention
The present invention relates to a binder-free conductive ink composition, conductive cage architecture, and fabrication process for wireless antenna which decreases its metallic filler content of conductive ink but still maintains high conductivity.
Description of the Prior Art
Conductive inks for printing process like screen printing and inkjet printing are so expensive that the utilization of printing process cannot prevail over metal-etching process that result in high cost and poisonous pollution.
Metals like silver, nickel and copper as the conductive materials are the key reason why the price of conductive ink remains very high. How to cut down on the metal amount and still maintain the resistance is the key issue.
On the other hand, high sintering temperature of metals often confines the choices of substrates and application.
In the coming age of internet of things, wireless devices with antennas play an important role. Traditional antenna in devices is made of copper or aluminum by etching process. The process is not only expensive but also produces many high-pollution wastes. In addition, etching process also confines the choices of substrates. Therefore, printing processes such as screen printing and inkjet printing catch the spotlight recently.
Although printing processes are cost-saving and eco-friendly. The conductive inks in printing process are very expensive, and may suffer from poor stability or limited life time. Conductive materials in the conductive inks are made of metals like silver, nickel, and copper. Compared to carbon species, metallic conductors are both high-priced and have potential oxidation problems.
U.S. Pat. No. 7,763,187 disclosed that CNT (buckyballs, and graphene were also alternatively used) was proposed to bridge the gap between separated silver. The CNT-reinforced silver ink showed greater mechanical, electrical, and thermal properties. In this patent, silver content is 2 to 95 wt %.
U.S. Pat. No. 8,709,187 disclosed that aqueous silver ink for use in RFID was proposed. Sheet resistance can be as low as 120 mohm/sq (˜24 mohm/sq/mil), by which the read range was at least 3 meter. Carbon, typically carbon black and graphite, may also be used as conductive materials. Silver content is about 50 to 70 wt % of the composition, and resins is about 4 to 10 wt %.
CN Publication No. 103436099 taught that a low-cost silver/carbon ink was proposed for screen printing. Ink consists of 55 to 72 wt % of C/Ag composites and 10 to 25 wt % of conductive resins. Coating can be dried under 130° C. to 150° C. Cost was said to save 30%.
CN Publication No. 101650982A disclosed a silver-based conductive ink. Ink mainly consists of 1-25 wt % polymer resins, 20-55 wt % silver powders, 0-8 wt % graphite, 20-60 wt % solvent, and other additives. Graphite power can be used as auxiliary conductive filler to reduce the cost of ink.
Furthermore, CN Publication No. US2010000441A1 taught that the graphene preparation and the graphene-based conductive inks comprising other fillers for electrically and thermally conductive application.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.